The present invention relates, in general, to the storage of blood and blood components. More particularly, it is directed to improvements in the storage of blood platelets for enhancing in vivo viability by storing the platelets in gas permeable containers in an oxygen-enriched atmosphere.
Because of the limited supply of whole blood available from donors, it has become the practice to fractionate whole blood into various of its component parts, e.g., plasma, platelets and erythrocytes. In this manner, patients in need of treatment by a particular blood component will be given only that component rather than whole blood. Thus, the limited supply of whole blood can be more efficiently used in the treatment of a larger number of people.
One factor, however, which limits the benefits of blood fractionation is the limited storage time possible for many blood components. If stored too long, a substantial reduction in the in vivo activity occurs, and thus the effectiveness of the treatment is compromised. Blood platelets, in particular, which assist in blood clotting, have been found to have a very limited storage life, typically less than about seventy-two hours. On the other hand, the medical usage of blood platelets, such as in the treatment of thrombocytopenia, has been on the increase. Accordingly, there is a continuing desire to improve and lenghten the storage time possible for blood platelets.
Although a number of elements have been identified as affecting the viability of platelets during storage, pH has been recognized as one of the best correlatives of in vivo platelet viability. In particular, in a paper entitled "Platelet Storage at 22.degree. C.: Role of Gas Transport Across Plastic Containers in Maintenance of Viability", by Murphy and Gardner, in Blood, 46:209, 1975, a pH range of generally between 6 and 7.6 was indicated as being preferred for storage at 22.degree. C. (72.degree. F.). Beyond this range of pH, a disc-to-sphere morphology change occurs which results in marked loss of platelet in vivo activity. The authors report that such deleterious pH changes, particularly into the acidic range, can be delayed if platelets are stored in containers constructed of a material such as polyethylene which is more permeable to O.sub.2 and CO.sub.2 than conventional containers made of 0.015 inch thick polyvinyl chloride. Polyethylene containers were disclosed in exhibit an O.sub.2 transport rate approximately twice as rapid as that across polyvinyl chloride. The authors suggest, however, that the improved platelet activities obtained in polyethylene containers also could be achieved by the use of thin polyvinyl chloride, (0.008 inches in thickness) since the rate of gas transport across plastic is inversely proportional in a linear fashion to the plastic's thickness. In addition, the authors disclose that storing platelets in polyethylene bags under a 10% CO.sub.2 -in-air atmosphere further improves the viability of the stored platelets.
While platelet viability is enhanced by the use of thin-walled polyvinyl chloride containers having enhanced O.sub.2 and CO.sub.2 permeability, such containers are not without disadvantages. Quality control during the manufacture of the bags becomes more critical than ever because of the greater risk that defects in the thin film may create an opening for microbial entry into the bag. The bags must be handled with greater care during use for the same reason. Further, it would be desirable if conventional bags of low gas permeability could continue in use.